In a typical document handler of the type often used with image input terminals such as those used for providing an electronic digital image (e.g., raster input scanners) or light-lens optical imaging system for imaging an original image and exposing a recording media, a sheet-like member hereinafter referred to as a document is transported from a document input station to an imaging station.
The transport of the document from the document input station to the imaging station generally is accomplished by a series of belts and/or rollers which engage the document to move it along a predetermined path in a registered fashion. The registered document is then delivered to a friction belt which moves the document over the imaging station surface to an imaging position on the imaging station surface hereinafter referred to, generally, as the platen.
When using a properly adjusted image input terminal to image documents on a platen, optimum results are provided when the document is presented parallel to the platen, and, generally, flush against the platen. Thus, any rippling of the document or any portions of the document outside the normal range of the scanner (e.g., the belt or portions thereof to which the sheet-like material adheres is away from the belt) results in a poor image.
This problem has become even more severe with time, as optical imaging systems and even electronic imagers are using systems which have a relatively short conjugate length. The use of such lenses or optically effective systems enhances imaging quality and reduces the size of such systems. Nevertheless, there are sacrifices, as there is the loss of the "forgiveness" of a longer conjugate length input system. Thus, the areas, where these problems exhibit themselves most often, are the portions of the documents away from the center of the imaging area of the platen, because as the distance from the center of the imaging area increase, the shorter conjugate length of the imaging systems cannot compensate for distances the sheet-like material may be lifted off the platen. Thus, even slight bunching of the sheet-like material or raising of the sheet-like material in the margin areas of the image input system result in a faulty input image received by the imaging system.
The use of friction belts to transport documents and other like sheet material across the platen presents several competing constraints. First, the belt and sheet-like material must have a high degree of adherence, compared to that between the sheet-like material and the platen and between the belt and the platen. Further, the wear on the materials of the belt, documents, and the platen should be minimized. It is also desirable to reduce the load on the motors which drive the belt, so that less powerful motors can be used to further reduce costs and/or maintenance time. As seen above, proper registration of the document on the platen is imperative in the vertical direction.
Proper registration of the document in the horizontal plane is also critical, as failure to maintain the registration of the sheet-like material, as it moves with the belt, generally results in a faulty image (Portions in non-imageable areas, skewed orientation, and the like).
Thus, the friction between the belt and paper must be greater than the friction between the paper and the platen and between the belt and the platen. These constraints exist because the sheet-like material must not stack, slip, hesitate or otherwise buckle as it moves on the belt across the platen. Otherwise, documents would frequently be presented in a non-registered condition at the imaging station.
To summarize these points, document handling systems must, therefore, move the sheet-like material without it slipping and sticking of the sheet-like material relative to the belt. It is preferred to have a system which also reduces belt and motor wear. Yet, it is also desired to increase the part life of the belt and motor and to reduce costs generally. The problems of wavy-line copies and out-of-focus copies of prior systems have become more acute as shorter conjugate optics are used to reduce the size and increase the effectiveness of input imaging terminals in copiers and scanners. These faulty copies result generally from a buckling of the document away from the platen or the document being held on the belt away from the platen. Thus, maintaining a document to be imaged in a flat attitude relative to the platen and proximate to the platen are necessary to avoid optical distortion and retain the document in focus.
The mechanical pressure members most often used to bear upon friction belts are elongated rollers which bear on the friction belt. Unfortunately, these rollers often cause several undesirable effects. First, they tend to be separated by a distance so that wavy, out of focus lines occur too frequently on copies produced from the image recorded by the image input terminal. These roller members also tend to bear relatively heavily on the portion of the platen over which they are positioned causing wear of the platen. This is unacceptable, since platens are often optically coated to achieve imaging performance or coated with a transparent film to reduce paper drag,. It also is wasteful, even for non-coated platens, because it reduces the useful life of the platen and also the quality of the images produced also decreases with time. Further, the area of the belt opposite the platen and at the extreme ends of the rollers often build up dirt. This results in darkening of copies produced thereby.
Various techniques have heretofore been used to provide a pressuring loaded to a friction belt in a document handler, as illustrated by the following disclosures, which may be relevant to certain aspects of the present invention:
U.S. Pat. No. 3,988,019 PA1 Patentee: Achelpohl PA1 Issued: Oct. 26, 1976 PA1 U.S. Pat. No. 4,669,721 PA1 Patentee: Westover PA1 Issued: Jun. 2, 1987 PA1 U.S. Pat. No. 4,190,185 PA1 Patentee: Thate PA1 Issued: Feb. 26, 1980 PA1 U.S. Pat. No. 3,937,454 PA1 Patentee: Colwill PA1 Issued: Feb. 10, 1976 PA1 Publication: Xerox Disclosure Journal PA1 Author: Thomas W. Taylor, et al. PA1 Issue: Vol. 7, No. 6, Nov./Dec. 1982
The relevant portions of the foregoing patents may be briefly summarized as follows:
U.S. Pat. No. 3,988,019 discloses an apparatus for depositing flat flexible articles on one double belt conveyor to another double belt conveyor by two ski like members. The members cooperating to push the cuticle down and of the first double belt conveyor to the second belt conveyor.
U.S. Pat. No. 4,669,721 discloses a sheet transporting apparatus which has a belt and a flexible elongated guide between which sheets pass. The flexible guide bears upon the sheet to maintain it proximate to belt to move the sheet between the belt and guides which may be a singular piece of several parallel members.
U.S. Pat. No. 4,190,185 discloses a first and second conveyor belt for transporting sheet material. The central portion of he sheet material is intended to be unsupported and not in contact with the belt. Engagement elements 3 engages the edges of the sheet to tension it and urge it into a planar flattened condition.
U.S. Pat. No. 3,937,454 discloses document recirculator for feeding documents over a platen. The belt is maintained in close proximity to the platen for moving documents by a fixed plate over the belt and inflatable bladder positioned between the plate and the belt.
Volume 7, No. 6, of the Xerox Disclosure Journal discloses a ski-like member which is mounted to a scuffer wheel to effect registration of a document. The scuffer wheel is so mounted to the ski-member that buckling of the document reduces the force applied by the scuffer wheel to the document.
All references cited in this specification, and their references, are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.